The invention relates to a pressing device for forming steel sheet blanks into clips, which comprise curved planking elements and rectilinear stringer elements, for connecting a fuselage cell skin to a stringer and an annular rib in an aircraft fuselage.
The fuselage cell of an aircraft is generally formed from a large number of fuselage barrels arranged behind each other and connected to each other in the sectional design still used conventionally. The fuselage barrels are formed with a large number of annular ribs spaced relative to each other. The ribs are planked with curved aluminum alloy sheet for the formation of the fuselage cell skin. A large number of reinforcing profiles (“stringers”) are arranged parallel to the longitudinal extension of the fuselage barrel on the inner surface of the fuselage cell skin such that they are uniformly spaced around the circumference. The mechanical connection between the stringers, the annular ribs and the fuselage skin is made by means of clips. The clips have a rectilinear stringer element for contact with the stringers and a planking element for contact with the curved fuselage cell skin.
Conventional clips are produced from a cut flat steel sheet blank of an aluminum alloy material in two bending steps. Forming is carried out by means of a rubber forming tool or with a membrane tool. Before the actual forming process, the steel sheet blanks are first soft annealed to guarantee easy mechanical deformability. After the two-stage forming process, the formed steel sheet blanks are solution heat treated in order to regain the required mechanical strengths. This is followed by further machining steps, such as application of the surface protection.
A disadvantage of existing production methods and the devices used for them is the relative large number of production steps, the low degree of automation and the thermal pre- and post-treatment of the steel sheet blanks previously required.